Currently, PPP access technique has already become a main method of broadband access application, especially the technical criterion of the PPP Over Ethernet (PPPoE) which is widely supported has become a preferred access method of broadband access operators.
FIG. 1 shows IP address assignment procedure used for a PPP session, which is implemented by a broadband access server. In PPP session an IP address is assigned by the server after an AAA (Authentication, Authorization, Account) client authentication is completed, and is released by the AAA client after an accounting-stop request or an accounting-reject request is sent. An accounting-start request is sent after a negotiation of PPP Internet Protocol Control Protocol (PPP IPCP) has completed, and the accounting-stop request may be sent only after the accounting-start request being sent. The accounting-reject request is sent before the accounting-start being sent when an exception occurs in the PPP session. The accounting-reject request does not send an accounting packet to a server of Remote Authentication Dial In User Service (RADIUS), as it is a mere local exception processing procedure, but not a RADIUS protocol standard.
However, unexpected dispersion of IP address used for PPP session occurs frequently when the broadband access server providing the PPP access service to result in the fact that IP address available for customer decrease, even no available IP address to be used. The problem of the prior art is caused due to the complexity of a PPP state machine. After the negotiation phase and authorization phase of the Link Control Protocol (LCP) are completed, the server has already assigned an IP address for a customer. Therefore, an oscillation of a LCP state machine and a IPCP state machine may be caused once a negotiation packet of LCP and IPCP is sent again, that is, a PPP session may be authenticated again and again if it may be negotiated repeatedly. In the case of the repeat for the authentication of PPP session, a customer may be assigned many IP addresses to be unexpected, which is called unexpected dispersion of IP address. There is not any available solution for settling this problem of the prior art in current PPP protocol and other protocol standards.